ex_09_3_3.py

#!/usr/bin/python
#AUTHOR: alexxa
#DATE: 27.12.2013
#SOURCE: Think Python: How to Think Like a Computer Scientist by Allen B. Downey
# http://www.greenteapress.com/thinkpython/html/index.html
#PURPOSE: Chapter 9. Case study: word play

#STATUS: Check for refactoring

# Exercise 9.3.3
# Can you find a combination of 5 forbidden letters that 
# excludes the smallest number of words?

# i.e. we need to find five most rare letters: 
# 1. Create a string of all words from words.txt -> build_string() function
# 2. Build a dictionary of letters' frequency -> words_frequency() function
# 3. Return 5 letters with the smallest frequency as a string/list -> words_popularity()

import time

def build_string():
    string = ''
    #print('Hello')
    fin = open('words.txt')
    for line in fin:
        word = line.strip()
        string = string + word
    #print(string)
    return string

def words_frequency():
    '''
        This function calculates letters frequency and
        returns it as a dictionary.
    '''
    alphabet = 'abcdefghijklmnopqrstuvwxyz'
    string = build_string()
    dictionary = {}
    for i in alphabet:
        dictionary[i] = dictionary.get(i, string.count(i))
    return dictionary


def words_popularity():
    '''
        This function returns the 5 most
         rarely-used words in the text
    '''
    dictionary = words_frequency()    
    #print(dictionary)
    dict_copy = dictionary
    counter = 0
    popular_words = []
    while counter < 5:
        popular_word = min(dict_copy, key=dict_copy.get)
        popular_words.append(popular_word)
        dict_copy.pop(popular_word, None)
        counter += 1
    return popular_words
    
    
start_time = time.time()
print('The 5 most rarely-used words in the text: {}'.format(words_popularity()))
function_time = time.time() - start_time

print('Running time is {0:.4f} s'.format(function_time))


  
#END